1. Field of the Invention
The present invention relates generally to fuel vapor emission control for fuel systems in vehicles with internal combustion engines. More particularly, the present invention relates to fuel tank fuel vapor emission control in such vehicles.
2. Description of the Related Art
Modern transportation vehicles which employ a liquid fuel for internal combustion engines conventionally also employ for storage of the liquid fuel a fuel tank. Similarly, since most liquid fuels are highly volatile, such a fuel tank typically contains in addition to the liquid fuel a fuel vapor. A concentration of fuel in the fuel vapor within the fuel tank is generally related to the temperature of the liquid fuel and the temperature of the fuel vapor.
While the fuel vapor within a fuel tank does not typically impair operation of a transportation vehicle powered by an engine which employs a liquid fuel extracted from the fuel tank, upon refueling of the fuel tank with additional liquid fuel the fuel vapor must of necessity be displaced. For environmental protection purposes and for economic reasons, it is desirable for such displaced fuel vapor not to be released into the atmosphere.
Various apparatus, systems and methods have been disclosed within the art of fuel system design for attenuating, upon refueling of a fuel tank, release of fuel vapor into the atmosphere. Well known in this regard are fuel system designs which incorporate the use of carbon filled canisters for cyclical absorptive capture and desorptive controlled release of fuel vapor displaced incident to refueling of a fuel tank. Examples of such fuel system designs are disclosed within U.S. Pat. No. 3,937,198, U.S. Pat. No. 5,456,238, U.S. Pat. No. 5,617,832 and Japan No. 4-124,449, all of which are incorporated herein fully by reference.
While any of the disclosed fuel system designs provides upon refueling of a fuel tank and during operation of the vehicle between refueling with a liquid fuel an attenuated displaced fuel vapor release into the atmosphere, such desirable result is often achieved only with complicated piping and valving schemes. In addition, carbon canisters have limited capacity for attenuating vapor release between refuelings.
There thus exists within the art of fuel tank design and fuel system design a continuing need for comparatively simple apparatus, systems and methods for attenuating release of a displaced or evolved fuel vapor into the atmosphere. It is towards that object that the present invention is directed.
In order to realize the object towards which the present invention is directed, the present invention provides in the first instance a fuel system comprising a fuel tank within which is contained a fuel vapor. The fuel tank is also fabricated to have a refueling detection means which is activated incident to refueling the fuel tank with a liquid fuel. The fuel system also has a fuel vapor valve which is activated by the refueling detection means, wherein: (1) the fuel vapor valve directs the fuel vapor displaced from the fuel tank to a first fuel vapor conduit connected to a fuel vapor absorption means when the refueling detection means is activated; and (2) the fuel vapor valve directs the fuel vapor from the fuel tank to a second fuel vapor conduit connected to an engine which is powered by the liquid fuel when the refueling detection means is not activated. Within the present invention, the second fuel vapor conduit does not incorporate a fuel vapor absorption means, in particular as interposed between the fuel vapor valve and the engine.